Optimise previews for large files.

[Mihai Glonț]

We should load large files progressively and cap the amount of information from the file that gets rendered - after all, it's just a preview.

It would also be beneficial to cache the data that we read so that the user does not have to wait every time a large file is clicked.

See http://wwwdev.ebi.ac.uk/biomodels/model-repository/model/277#Files